Can you login to your account to make sure there's nothing unusual there. It's likely you will not find anything unusual, but rule out the easy to check stuff anyway. If you have another phone, try the SIM card there and see if it works. My suspicion is you have some sort of intermittent fault on the phone. Even if the SIM card connects for a moment that shows the fault isn't there. There's no known issues with the network. BTW, what model of phone is giving you the problems. We can do some online searches for reported intermittent connection problems.
